I own a 456 that has two vacu flush heads, one of they has a strange issue, even when the holding tank is empty it back flushes black water overboard from the holding tank vent, how can this happen if the tank is not full, We flush the head, then we hear the vacum pump running building pressure, then we hear liquid running thru the vent? Any ideas?
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The tank has to be full. And if the vacuum pump is building pressure in the holding tank, it can only mean that the tank vent is blocked. The tank is so pressurized that a trickle of waste can be forced out, but it's not allowing any air in or out.
A holding tank vent has two functions: 1. it provides an escape for air in the tank displaced by incoming waste, and 2. it provides a source of air into the tank to replace contents as they're pumped out. If no air can get out, the tank becomes pressurized...if none can come in, the pumpout or macerator pulls a vacuum that prevents waste from being pulled out. So while you may have gone through the motions of pumping out or dumping the tank, it's still full.
If there's a vent filter in the vent line, that's almost certain to be your culprit. Vent filters are very bad idea in all cases, and an even worse idea on a sailboat...'cuz sailboats heel, and when they heel, waste can spill into the vent...and when that happens, the charcoal in filter gets wet, swells and blocks the vent. The solution: get rid of the d'd filter! However, before you remove it, it would be a VERY good idea to open the deck pumpout cap to relieve any pressure in the system.
If there is no filter, the two most common places for a vent blockage to occur are the vent thru-hull and the connection to the tank--both the tank fitting and that end of the vent hose. First, check the thru-hull...use a screwdriver--or whateverr works--to scrape out what you find. If there's a screen in the thru-hull, knAnd ock it out...screens cause more problems than they solve. If this clears the blockage, there's likely to be a spew, so watch where you stand and have a hose at the ready.
Next, remove the vent line from the tank...scrape out the tank fitting and the end of the hose (again, open the deck cap first!).
Once you've solved this problem, you need to start maintaining your system to prevent future problems...'cuz prevention is always easier and cheaper than cure.
Peggy--- OK, I also have a 456 and 1 of the macerator pumps seems to be plugged. It has a high pitched sound followed by the breaker popping after ~1 min. Also, I do see big "bubbles" coming from under the boat when I "try" to use it. Thanks...
Tank vent is the first thing I'd check here too
'Cuz if the macerator is pulling a vacuum, it would account for your symptoms.
Are we talking about an impeller macerator pump or an electric diaphragm pump? If an impeller macerator pump, letting it run for a full minute without anything going through it will "fry" the impeller, especially if you've done that repeatedly. So at the very least, you're gonna have to replace the impeller.
If it's not the tank vent, I suspect a guest has flushed something they shouldn't have, that somehow made it all the way into the tank and has jammed the discharge pump. If THAT;s the case, you're gonna have to clean out the pump...in which case I hope there's a y-valve in your tank discharge line instead of only a tee.
Try pumping out...that will tell you whether the vent is blocked. Just make sure the tank really is empty before assuming that it's not...'cuz it will be possible to pull out a gallon or two before the pump pulls a vacuum. Then thoroughly rinse out the system before getting into the discharge pump.
'Cuz if the macerator is pulling a vacuum, it would account for your symptoms.
Are we talking about an impeller macerator pump or an electric diaphragm pump? If an impeller macerator pump, letting it run for a full minute without anything going through it will "fry" the impeller, especially if you've done that repeatedly. So at the very least, you're gonna have to replace the impeller.
If it's not the tank vent, I suspect a guest has flushed something they shouldn't have, that somehow made it all the way into the tank and has jammed the discharge pump. If THAT;s the case, you're gonna have to clean out the pump...in which case I hope there's a y-valve in your tank discharge line instead of only a tee.
Try pumping out...that will tell you whether the vent is blocked. Just make sure the tank really is empty before assuming that it's not...'cuz it will be possible to pull out a gallon or two before the pump pulls a vacuum. Then thoroughly rinse out the system before getting into the discharge pump.
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